SHORT VIDEO INTRODUCTION

• Design is the most important part of the program development cycle
• Understand the task that the program is to perform
  • Work with customer to get a sense what the program is supposed to do
  • Ask questions about program details
  • Create one or more software requirements

• Determine the steps that must be taken to perform the task
  • Break down required task into a series of steps
  • Create an algorithm, listing logical steps that must be taken
• Algorithm: set of well-defined logical steps that must be taken to perform a task

Pseudocode

• Pseudocode: fake code read more
  • Informal language that has no syntax rule
  • Not meant to be compiled or executed
  • Used to create model program
    • No need to worry about syntax errors, can focus on program’s design
    • Can be translated directly into actual code in any programming language.

Flowchart

• Flowchart: diagram that graphically depicts the steps in a program read more
  • Ovals are terminal symbols
  • Parallelograms are input and output symbols
  • Rectangles are processing symbols
  • Symbols are connected by arrows that represent the flow of the program

Friendship Algorithm

IPO

• Typically, computer performs three-step process
  • Receive input
    • Input: any data that the program receives while it is running
  • Perform some process on the input
    • Example: mathematical calculation
  • Produce output

Related Concept

• Function: piece of prewritten code that performs an operation
• print function: displays output on the screen
• Argument: data given to a function
  • Example: data that is printed to screen
• Statements in a program execute in the order that they appear
• From top to bottom

Strings and String Literals

• String: sequence of characters that is used as data
• String literal: string that appears in actual code of a program
  • Must be enclosed in single (’) or double (“) quote marks
  • String literal can be enclosed in triple quotes (’’’ or “““)
    • Enclosed string can contain both single and double quotes and can have multiple lines

Comments

• Comments: notes of explanation within a program
  • Ignored by Python interpreter
    • Intended for a person reading the program’s code
  • Begin with a # character
• End-line comment: appears at the end of a line of code
  • Typically explains the purpose of that line

Overview

name = "chad"
age = 20
print(age, name)

20 chad

• In assignment statement, variable receiving value must be on left side
• A variable can be passed as an argument to a function
  • Variable name should not be enclosed in quote marks
• You can only use a variable if a value is assigned to it

Variable Naming Rules

• Rules for naming variables in Python:
  • Variable name cannot be a Python keyword
  • Variable name cannot contain spaces
  • First character must be a letter or an underscore
  • After first character may use letters, digits, or underscores
  • Variable names are case sensitive
  • Variable name should reflect its use

Displaying Multiple Items with the print Function

• Python allows one to display multiple items with a single call to print
  • Items are separated by commas when passed as arguments
  • Arguments displayed in the order they are passed to the function
  • Items are automatically separated by a space when displayed on screen

name = "chad"
age = 20
print("Hello", name+".", "I heard that you got", str(age)+"th", "birthday")

Hello chad. I heard that you got 20th birthday

Variable Reassignment

name = "chad"
print(name)

name = "Joe"
print(name)

name = 20
print(name)

chad
Joe
20

Numeric Data Types, Literals, and the str Data Type

num1 = 20
num2 = 20.54
num3 = "20.68"
print(num1)
print(num2)
print(num3)

20
20.54
20.68

Reassigning a Variable to a Different Type

• A variable in Python can refer to items of any type

Overview

Most programs need to read input from the user

• Built-in inputfunction reads input from keyboard
  • Returns the data as a string
  • Format: variable = input(prompt)
    • prompt is typically a string instructing user to enter a value
  • Does not automatically display a space after the prompt

Overview

print(1+2)
print(58-782)
print(35*72)
print(4/2)
print(4//2)
print(5//2)
print(((1+2) * (58-782)) / 35*72)

3
-724
2520
2.0
2
2
-4468.114285714286

Operator Precedence and Grouping with Parentheses

Python operator precedence:

• Operations enclosed in parentheses
  • Forces operations to be performed before others
• Exponentiation (**)
• Multiplication (*), division (/ and //), and remainder (%)
• Addition (+) and subtraction (-)
  • Higher precedence performed first
  • Same precedence operators execute from left to right

The Exponent Operator and the

print(4**2)
print(4^2)
print(4%2)
print(5%2)

16
6
0
1

Converting Math Formulas to Programming Statements

• Operator required for any mathematical operation
• When converting mathematical expression to programming statement:
  • May need to add multiplication operators
  • May need to insert parentheses

Mixed-Type Expressions and Data Type Conversion

print(10 + 11)
print(10.1 + 11.3)
print(10.1 + 11)
print(float(10)+11)
print(int(12.1235845865))

21
21.4
21.1
21.0
12

Breaking Long Statements into Multiple Lines

• Long statements cannot be viewed on screen without scrolling and cannot be printed without cutting off
• Multiline continuation character (\): Allows to break a statement into multiple lines

result = var1 * 2 + var2 * 3 + \
var3 * 4 + var4 * 5

• Any part of a statement that is enclosed in parentheses can be broken without the line continuation character.

print("Monday's sales are", monday, "and Tuesday's sales are", tuesday, "and Wednesday's sales are", Wednesday)
total = (value1 + value2 + value3 + value4 + value5 + value6)

Syntex

• To append one string to the end of another string
• Use the + operator to concatenate strings

message = 'Hello' + 'world'
print(message)

Helloworld

• You can use string concatenation to break up a long string literal

print('Enter the amount of ' + 'sales for each day and ' + 'press Enter.')

Enter the amount of sales for each day and press Enter.

Implicit String Literal Concatenation

• Two or more string literals written adjacent to each other are implicitly concatenated into a single string

my_str = 'one' 'two' 'three'
print(my_str)

onetwothree

print('Enter the amount of ' 'sales for each day and ' 'press Enter.')

Enter the amount of sales for each day and press Enter.

Overview

Overview

print(f'Hello world')

Hello world

name = 'Johnny'
print(f'Hello {name}.')

Hello Johnny.

Magic Numbers

• A magic number is an unexplained numeric value that appears in a program’s code.
• Example:

amount = balance * 0.069

• What is the value 0.069? An interest rate? A fee percentage? Only the person who wrote the code knows for sure.

The Problem with Magic Numbers

• It can be difficult to determine the purpose of the number.
• If the magic number is used in multiple places in the program, it can take a lot of effort to change the number in each location, should the need arise.
• You take the risk of making a mistake each time you type the magic number in the program’s code.
  • For example, suppose you intend to type 0.069, but you accidentally type .0069. This mistake will cause mathematical errors that can be difficult to find.

Named Constants

• You should use named constants instead of magic numbers.
• A named constant is a name that represents a value that does not change during the program’s execution.
• Example:

INTEREST_RATE = 0.069

• This creates a named constant named INTEREST_RATE, assigned the value 0.069. It can be used instead of the magic number:

amount = balance * INTEREST_RATE

Advantages of Using Named Constants

• Named constants make code self-explanatory (self-documenting)
• Named constants make code easier to maintain (change the value assigned to the constant, and the new value takes effect everywhere the constant is used)
• Named constants help prevent typographical errors that are common when using magic numbers

Overview

• Python’s turtle graphics system displays a small cursor known as a turtle.

• You can use Python statements to move the turtle around the screen, drawing lines and shapes.

• To use the turtle graphics system, you must import the turtle module with this statement:

import turtle

This loads the turtle module into memory

Moving the Turtle Forward

• Use the turtle.forward(n)statement to move the turtle forward n pixels.

import turtle
turtle.forward(100)

Turning the Turtle

• The turtle’s initial heading is 0 degrees (east)
• Use the turtle.right(angle)statement to turn the turtle right by angle degrees.
• Use the turtle.left(angle)statement to turn the turtle left by angle degrees.

import turtle
turtle.forward(100)
turtle.left(90)
turtle.forward(100)

import turtle
turtle.forward(100)
turtle.right(45)
turtle.forward(100)

Setting the Turtle’s Heading

• Use the turtle.setheading(angle)statement toset the turtle’s heading to a specific angle.

import turtle
turtle.forward(50)
turtle.setheading(90)
turtle.forward(100)
turtle.setheading(180)
turtle.forward(50)
turtle.setheading(270)
turtle.forward(100)

Setting the Pen Up or Down

• When the turtle’s pen is down, the turtle draws a line as it moves. By default, the pen is down.
• When the turtle’s pen is up, the turtle does not draw as it moves.
• Use the turtle.penup()statement to raise the pen.
• Use the turtle.pendown()statement to lower the pen.

import turtle
turtle.forward(50)
turtle.penup()
turtle.forward(25)
turtle.pendown()
turtle.forward(50)
turtle.penup()
turtle.forward(25)
turtle.pendown()
turtle.forward(50)

Drawing Circles

• Use the turtle.circle(radius)statement to draw a circle with a specified radius.

import turtle
turtle.circle(100)

Drawing Dots

• Use the turtle.dot()statement to draw a simple dot at the turtle’s current location.

import turtle
turtle.dot()
turtle.forward(50)
turtle.dot()
turtle.forward(50)
turtle.dot()
turtle.forward(50)

Changing the Pen Size and Drawing Color

• Use the turtle.pensize(width)statement to change the width of the turtle’s pen, in pixels.
• Use the turtle.pencolor(color)statement to change the turtle’s drawing color.
  • See Appendix D in your textbook for a complete list of colors.

import turtle
turtle.pensize(5)
turtle.pencolor('red')
turtle.circle(100)

Working with the Turtle’s Window

• Use the turtle.bgcolor(color)statement to set the window’s background color.
  • See Appendix D in your textbook for a complete list of colors.
• Use the turtle.setup(width,height)statement to set the size of the turtle’s window, in pixels.
  • The width and height arguments are the width and height, in pixels.
  • For example, the following interactive session creates a graphics window that is 640 pixels wide and 480 pixels high:

import turtle
turtle.setup(640, 480)

• The turtle.clearscreen()statement:
  • Erases all drawings that currently appear in the graphics window.
  • Resets the drawing color to black.
  • Resets the turtle to its original position in the center of the screen.
  • Resets the graphics window’s background color to white.

Working with Coordinates

• The turtle uses Cartesian Coordinates

Moving the Turtle to a Specific Location

• Use the turtle.goto(x, y)statement to move the turtle to a specific location.

import turtle
turtle.goto(0, 100)
turtle.goto(−100, 0)
turtle.goto(0, 0)

• The turtle.pos() statement displays the turtle’s current X,Y coordinates.
• The turtle.xcor() statement displays the turtle’s current X coordinate and the turtle.ycor() statement displays the turtle’s current Y coordinate.

Animation Speed

• Use the turtle.speed(speed)command to change the speed at which the turtle moves.
  • The speed argument is a number in the range of 0 through 10.
  • If you specify 0, then the turtle will make all of its moves instantly (animation is disabled).

Hiding and Displaying the Turtle

• Use the turtle.hideturtle()command to hide the turtle.
  • This command does not change the way graphics are drawn, it simply hides the turtle icon.
• Use the turtle.showturtle()command to display the turtle.

Displaying Text

• Use the turtle.write(text)statement to display text in the turtle’s graphics window.
  • The text argument is a string that you want to display.
  • The lower-left corner of the first character will be positioned at the turtle’s X and Y coordinates.

import turtle
turtle.write('Hello World')

Filling Shapes

• To fill a shape with a color:
  • Use the turtle.begin_fill()command before drawing the shape
  • Then use the turtle.end_fill()command after the shape is drawn.
  • When the turtle.end_fill()command executes, the shape will be filled with the current fill color

import turtle
turtle.hideturtle()
turtle.fillcolor('red')
turtle.begin_fill()
turtle.circle(100)
turtle.end_fill()

Getting Input With a Dialog Box

import turtle
age = turtle.numinput('Input', 'Enter your age')

import turtle
name = turtle.textinput('Input', 'Enter your name')

• Specifying a default value, minimum value, and maximum value with turtle.numinput:

import turtle
num = turtle.numinput('Input', 'Enter a number', default=10, minval=0, maxval=100)

• An error message will be displayed if the input is less than minvalor greater than maxval

Keeping the Graphics Window Open

• When running a turtle graphics program outside IDLE, the graphics window closes immediately when the program is done.
• To prevent this, add the turtle.done()statementto the very end of your turtle graphics programs.
  • This will cause the graphics window to remain open, so you can see its contents after the program finishes executing.